[pypy-dev] Avoiding code duplication

[Antonio Cuni]

Hi Armin, hi all

Armin Rigo wrote:
> A different comment: as you mentioned on IRC it would be nice if the
> back-end could choose which methods it implements natively.  At one
> point there was the idea that maybe the 'oopspec' attributes that
> started to show up in lltypesystem/rlist.py (used by the JIT only) could
> be useful in this respect.  If I remember correctly, the idea didn't
> work out because of the different 'lowleveltype' needed, and the
> difference in the interface.  Merging the ADT method names of lltyped
> lists and the GENERIC_METHODS of ootyped lists could be a step in this
> direction again.  The interesting point is that each oo back-end could
> then choose to special-case the ll_xxx() functions with the oopspecs
> that they recognize, and just translate the other ones normally.  (The
> ll back-ends always translate them all.)

I have successfully moved almost all ll_* helpers from 
rpython/lltypesystem/rlist.py to rpython/rlist.py so that now they are 
shared between the two typesystems.

For doing that I had to extend the ADT interface of ListRepr to include 
_ll_resize_ge and _ll_resize_le, as well as to add the same function as 
_GENERIC_METHODS in ootypesystem.

Now ootypesystem should support the full list's semantic but in a 
far-from-perfect way: the main issue is that most operations are done by 
the ll_* helpers, even when there could be a more efficient native 
equivalent.

I see three main ways of fixing that:

1) further extend the ADT/_GENERIC_METHODS interface to include common 
operations that could be natively available in OO targets and modify 
ll_* helpers to use that methods; e.g., we could insert a "remove_range" 
and let ll_listdelslice & co. using it. This way OO backends could 
easily forward call to remove_range to the runtime; moreover if the 
inliner works well there should be no performance penalties for 
lltypesystem;

2) follow Armin's suggestion to use oopspec for letting backends 
forwarding to the RTE only what they want;

3) a mixture of 1 and 2.

ciao Anto